Photoelectric sensors are a great choice for packaging, material handling, automotive, and many other applications. They use a light emitter, a light receiver, and a lens for detection. Photoelectric sensors are often the go-to sensor, when an inductive sensor does not fit the application. They are incredibly useful for detecting a variety of objects, but it is important to be aware of their limitations.
1. Know your environment
Photoelectric sensors have a lens and in a clean environment, this is not an issue. However, a dirty environment can lead to a dirty lens, which interferes with proper operation. Thus, maintenance and regular cleaning is necessary. Thru beam models normally require less maintenance due to high gain. High gain allows the light to burn through dirt and dust, but eventually the lens still needs to be cleaned. Ultrasonic sensors are a useful alternative. They work well in dirty environments, because they don't have a lens and don’t require regular cleaning to remain operational.
2. Know your target
Basic, diffuse mode photoelectric sensors may not perform consistently if the targets vary in color. One color might be easier to recognize than another color, and detection of clear objects may not be possible. Diffuse mode with background suppression and other types of advanced photoelectric sensors exist for color detection and clear object detection. Clear object sensors detect transparent targets and background suppression sensors detect targets regardless of color. For even more flexibility, color sensors can identify minute color variations between targets. Color sensors can be taught up to three colors and can distinguish one color from another. Depending on the application, an ultrasonic sensor is another good option. An ultrasonic sensor reliably detects clear objects and objects of various colors, but it cannot differentiate between them.
3. Avoid cross-talk
If multiple photoelectric sensors are used in close proximity to each other, there is the possibility of one sensor confusing another sensor's output as its own. Overcoming cross-talk is typically not difficult. Allowing more distance between the sensors is an easy fix. In applications where the sensors must be near each other, use a model with built-in cross-talk protection. Using sensors that operate at different frequencies is another way to prevent cross-talk.
4. Know your light source
Photoelectric sensors are available with various light sources. LED light sources are the most common, and provide a larger light spot. To detect very small objects, a laser light source would most likely be used because of its very small light spot. LED light sources and Class 1 lasers are not at all damaging to the human eye. Class 2 lasers are also eye safe, as long as you do not stare directly at them. Consider your application, and choose an appropriate light source based on your needs.
5. Be aware of temperature
High temperatures can be an issue without the proper sensor. Photoelectric sensors are available in standard and high-temperature models. In high-temperature applications, it's best to use glass fiber-optic cable with stainless steel sheathing and high-temperature reflectors for retroreflective models. Using high-temperature products will ensure safe and reliable operation up to 900 °F (482 °C).